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<p class="purpose">What to do to make use of the syntax module in a new command-line tool.</p>

<ul class="toc"><li><a href="P-htitm.html#SP1">&#167;1. Status</a></li><li><a href="P-htitm.html#SP2">&#167;2. Importing the module</a></li><li><a href="P-htitm.html#SP3">&#167;3. Using callbacks</a></li></ul><hr class="tocbar">

<p class="commentary firstcommentary"><a id="SP1" class="paragraph-anchor"></a><b>&#167;1. Status.</b>The syntax module provided as one of the "services" suite of modules, which means
that it was built with a view to potential incorporation in multiple tools.
It can be found, for example, in <a href="../inform7/index.html" class="internal">inform7</a>, <a href="../inbuild/index.html" class="internal">inbuild</a> and <a href="../syntax-test/index.html" class="internal">syntax-test</a>,
among others. <a href="../syntax-test/index.html" class="internal">syntax-test</a> may be useful as a minimal example of a tool
using <a href="index.html" class="internal">syntax</a>.
</p>

<p class="commentary">By convention, the modules considered as "services" have no dependencies on
other modules except for <a href="../foundation/index.html" class="internal">foundation</a> and other "services" modules.
</p>

<p class="commentary">A tool can import <a href="index.html" class="internal">syntax</a> only if it also imports <a href="../foundation/index.html" class="internal">foundation</a> and
<a href="../words-module/index.html" class="internal">words</a>.
</p>

<p class="commentary firstcommentary"><a id="SP2" class="paragraph-anchor"></a><b>&#167;2. Importing the module.</b>We'll use the term "parent" to mean the tool which is importing <a href="index.html" class="internal">syntax</a>,
that is, which will include its code and be able to use it. As with any
imported module,
</p>

<ul class="items"><li>&#9679; The contents page of the parent's web must identify and locate the
module:
</li></ul>
<pre class="displayed-code all-displayed-code code-font">
<span class="element-syntax">Import</span><span class="plain-syntax">:</span><span class="string-syntax"> somepath/syntax</span>
</pre>
<ul class="items"><li>&#9679; The parent must call <span class="extract"><span class="extract-syntax">SyntaxModule::start()</span></span> just after it starts up, and
<span class="extract"><span class="extract-syntax">SyntaxModule::end()</span></span> just before it shuts down. (But just after, and just
before, the corresponding calls to <a href="../foundation/index.html" class="internal">foundation</a>.)
</li></ul>
<p class="commentary">But in addition, the parent of <a href="index.html" class="internal">syntax</a> must define some Preform grammar:
</p>

<ul class="items"><li>&#9679; <span class="extract"><span class="extract-syntax">&lt;language-modifying-sentence&gt;</span></span> to recognise sentences modifying the
language which is currently being parsed;
</li><li>&#9679; <span class="extract"><span class="extract-syntax">&lt;structural-sentence&gt;</span></span> to recognise structurally important sentences;
</li><li>&#9679; <span class="extract"><span class="extract-syntax">&lt;dividing-sentence&gt;</span></span> to recognise sentences which divide up the text,
normally headings;
</li><li>&#9679; <span class="extract"><span class="extract-syntax">&lt;comma-divisible-sentence&gt;</span></span> to recognise sentences where a comma plays
a role normally expected to be played by a colon.
</li></ul>
<p class="commentary">Though compulsory, these don't need to do much: see <a href="../syntax-test/1-ut.html" class="internal">Unit Tests (in syntax-test)</a>.
</p>

<p class="commentary firstcommentary"><a id="SP3" class="paragraph-anchor"></a><b>&#167;3. Using callbacks.</b>Shared modules like this one are tweaked in behaviour by defining "callback
functions". This means that the parent might provide a function of its own
which would answer a question put to it by the module, or take some action
on behalf of the module: it's a callback in the sense that the parent is
normally calling the module, but then the module calls the parent back to
ask for data or action.
</p>

<p class="commentary">The parent must indicate which function to use by defining a constant with
a specific name as being equal to that function's name. A fictional example
would be
</p>

<pre class="displayed-code all-displayed-code code-font">
<span class="plain-syntax">    </span><span class="function-syntax">@d</span><span class="plain-syntax"> EXPRESS_SURPRISE_SYNTAX_CALLBACK Emotions::gosh</span>

<span class="plain-syntax">    =</span>
<span class="plain-syntax">    </span><span class="element-syntax">void Emotions:</span><span class="plain-syntax">:</span><span class="string-syntax">gosh(text_stream *OUT) {</span>
<span class="plain-syntax">        WRITE("Good gracious!\n");</span>
<span class="plain-syntax">    }</span>
</pre>
<p class="commentary">The syntax module has many callbacks, but they are all optional. The following
alphabetical list has references to fuller explanations:
</p>

<ul class="items"><li>&#9679; <span class="extract"><span class="extract-syntax">AMBIGUITY_JOIN_SYNTAX_CALLBACK</span></span> can rearrange ambiguous readings as
added to a syntax tree: see <a href="2-st.html#SP21" class="internal">SyntaxTree::add_reading</a>.
</li><li>&#9679; <span class="extract"><span class="extract-syntax">ANNOTATION_COPY_SYNTAX_CALLBACK</span></span> can perform deep rather than shallow
copies of node annotations when these are essential: see <a href="2-na.html#SP12" class="internal">Annotations::copy</a>.
</li><li>&#9679; <span class="extract"><span class="extract-syntax">ANNOTATION_PERMISSIONS_SYNTAX_CALLBACK</span></span>, <span class="extract"><span class="extract-syntax">MORE_ANNOTATION_PERMISSIONS_SYNTAX_CALLBACK</span></span>
and <span class="extract"><span class="extract-syntax">EVEN_MORE_ANNOTATION_PERMISSIONS_SYNTAX_CALLBACK</span></span> gives permission for nodes
of given types to have annotations with given IDs, and effectively provides a
way to create custom annotations: see <a href="2-na.html#SP13" class="internal">Annotations::make_annotation_allowed_table</a>.
</li><li>&#9679; <span class="extract"><span class="extract-syntax">BEGIN_OR_END_HERE_SYNTAX_CALLBACK</span></span> is called when a new extension beginning
or ending sentence is found in the source text being broken into sentences:
see <a href="3-snt.html#SP7" class="internal">Sentences::make_node</a>.
</li><li>&#9679; <span class="extract"><span class="extract-syntax">DIVIDE_AT_COLON_SYNTAX_CALLBACK</span></span> is called to ask permission to break a
sentence at a colon. See <a href="3-snt.html#SP5" class="internal">Sentences::break_inner</a>.
</li><li>&#9679; <span class="extract"><span class="extract-syntax">IS_SENTENCE_NODE_SYNTAX_CALLBACK</span></span> is asked whether a given node represents
a regular sentence or not: see <a href="2-nt.html#SP11" class="internal">NodeType::is_sentence</a>.
</li><li>&#9679; <span class="extract"><span class="extract-syntax">LANGUAGE_ELEMENT_SYNTAX_CALLBACK</span></span> is called when a sentence is found matching
the nonterminal <span class="extract"><span class="extract-syntax">&lt;language-modifying-sentence&gt;</span></span>: see <a href="3-snt.html#SP7" class="internal">Sentences::make_node</a>.
</li><li>&#9679; <span class="extract"><span class="extract-syntax">LOG_UNENUMERATED_NODE_TYPES_SYNTAX_CALLBACK</span></span> is called to log a node type
not recognised as one of the enumerated <span class="extract"><span class="extract-syntax">*_NT</span></span> values: see <a href="2-nt.html#SP8" class="internal">NodeType::log</a>.
</li><li>&#9679; <span class="extract"><span class="extract-syntax">NEW_HEADING_SYNTAX_CALLBACK</span></span> is called when a new heading sentence is found
in the source text being broken into sentences: see <a href="3-snt.html#SP7" class="internal">Sentences::make_node</a>.
</li><li>&#9679; <span class="extract"><span class="extract-syntax">NEW_HEADING_TREE_SYNTAX_CALLBACK</span></span> is called when a new syntax tree is being
created, and needs to be given a matching tree of headings: see <a href="2-st.html#SP2" class="internal">SyntaxTree::new</a>.
</li><li>&#9679; <span class="extract"><span class="extract-syntax">NODE_METADATA_SETUP_SYNTAX_CALLBACK</span></span>, <span class="extract"><span class="extract-syntax">MORE_NODE_METADATA_SETUP_SYNTAX_CALLBACK</span></span>
and <span class="extract"><span class="extract-syntax">EVEN_MORE_NODE_METADATA_SETUP_SYNTAX_CALLBACK</span></span> adds new syntax tree node
types: see <a href="2-nt.html#SP12" class="internal">NodeType::metadata_setup</a>.
</li><li>&#9679; <span class="extract"><span class="extract-syntax">PARENTAGE_EXCEPTIONS_SYNTAX_CALLBACK</span></span> allows exceptions to the rules about
which nodes in a syntax tree can be parents of which other nodes: see
<a href="2-nt.html#SP13" class="internal">NodeType::parentage_allowed</a>.
</li><li>&#9679; <span class="extract"><span class="extract-syntax">PARENTAGE_PERMISSIONS_SYNTAX_CALLBACK</span></span>, <span class="extract"><span class="extract-syntax">MORE_PARENTAGE_PERMISSIONS_SYNTAX_CALLBACK</span></span>
and <span class="extract"><span class="extract-syntax">EVEN_MORE_PARENTAGE_PERMISSIONS_SYNTAX_CALLBACK</span></span> adds permissions for nodes
to be parents of each other: see <a href="2-nt.html#SP4" class="internal">NodeType::make_parentage_allowed_table</a>.
</li><li>&#9679; <span class="extract"><span class="extract-syntax">PROBLEM_SYNTAX_CALLBACK</span></span> is called when a syntax error is found, and can
prevent this from being issued to the terminal as an error message: see
<a href="3-snt.html#SP12" class="internal">Sentences::syntax_problem</a>.
</li><li>&#9679; <span class="extract"><span class="extract-syntax">NEW_NONSTRUCTURAL_SENTENCE_SYNTAX_CALLBACK</span></span> is called when a new, regular
sentence is found in the source text being broken into sentences: see
<a href="3-snt.html#SP7" class="internal">Sentences::make_node</a>.
</li><li>&#9679; <span class="extract"><span class="extract-syntax">UNKNOWN_PREFORM_RESULT_SYNTAX_CALLBACK</span></span> is used only by the Preform cache:
if this isn't being used, it's sufficient to return a null pointer. See
<a href="2-spc.html" class="internal">Simple Preform Cache</a>.
</li></ul>
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